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Ch 15. Group 15

Ch 15. Group 15. N 2 / O 2 separation. BP MW main uses N 2 77K 28 inert gas/coolant O 2 90K 32 fuel/medial. N 2 B(N ≡N) = 946 KJ/mol (kinetically inert) N 2 fixation: N 2 + 3 H 2  2 NH 3 Haber process, industrial source of all N compounds.

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Ch 15. Group 15

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  1. Ch 15. Group 15

  2. N2 / O2 separation BP MW main uses N2 77K 28 inert gas/coolant O2 90K 32 fuel/medial

  3. N2 B(N≡N) = 946 KJ/mol (kinetically inert) N2 fixation: N2 + 3 H2 2 NH3 Haber process, industrial source of all N compounds 400C, 200 atm, Fe cat Elemental Forms

  4. bacteria cat = nitrogenase N2 chemistry 6 Li + N2 2 Li3N [Ru(NH3)5(H2O)]2+ (aq)  Cat process to N cmpds? N2 NH4+ enzyme w/ Fe4S4 cage + MoFe7S8 cofactors (ferrodoxins)

  5. P allotropes black P white P Molecular, Td, rapidly oxidized to phosphate in air red P many polymorphs, air stable hexagonal puckered sheets prep from high P or Bi flux, air stable

  6. History From “The 13th Element: The Sordid Tale of Murder, Fire, and Phosphorus” by John Emsley

  7. Elemental forms As, Sb, Bi  incr. metallic character Single vs. multiple bonds D(E-E) D(E=E) D(E≡E) N 163 409 946 NN P 201 -P-P- O 142 447 O=O S 264 431 -S-S- generally in the p-block, -bonds are uncommon except with period 2 elements

  8. Halides almost all group 15 halides are air sensitive: PCl3 + ½O2 O = PCl3 oxidation PCl3 + 4H2O  H3PO4 + 3HCl + H2 oxidation + hydrolysis all pentahalides hydrolyze rapidly and generate HX N forms endoergic halides NF3 to “NI3” show decreasing stability NF4+ is isostructural to ammonium and is the only stable N(V) halide P to Bi MX3 MX5 MX6all are known for X = F, most for Cl, some for Br,I C3v D5h Oh

  9. Halides PF5 to BiF5 show increasing Lewis acidity ex : PF5 + F PF6ΔH = - 340kJ/mol SbF5 + F SbF6- 500kJ/mol SbF5 is an oligomeric, viscous, colorless liquid Heavier congeners tend to higher CN (SbF5)4

  10. Group 15 Frost diagrams

  11. Group 15 redox trends • NO3 and Bi(V) are strong oxidants • NO3should be the strongest oxidant from general periodic trend down a group (higher χ and higher IE result in less stable high oxidation state). But there is no regular trend. • Bi(III) is unusually stable due to inert pair effect • PO43 is unusually stable due to strong P=O bonding • Low pH increases oxidation strength of nitrogen oxoanions and also often increases rate (via protonation of N-O bonds) • most reactions are slow and many species are kinetically stable • ex: NO2 , N2O, NO, NO2  N2O4

  12. N oxides N2O4 is isoelectronic w C2O42 (oxalate). Since C has lower χthan N, oxalate has a stronger M-M bond and there is no appreciable equ w/ monomer

  13. N oxides

  14. N oxides 4 HNO3 (aq)  4 NO2 (aq) + O2 (g) + 2 H2O (l) More rapid for conc. HNO3 due to presence of undissociated acid Easier to break N-OH vs N=O N2O (g) + 2 H+ (aq) + 2 e- N2 (g) + H2O (l) E = + 1.77 V at pH = 0, but it’s a poor oxidant due to slow reaction kinetics NO+ (solv) + e- NO (g) E ~ + 1.1 V, nitrosyl cation is a facile oxidant with rapid kinetics

  15. Ox state -3 -1 -2 Ammonia hydroxylamine hydrazine pKb 4.8 8.2 7.9 Low oxidation state N also N3- (azide) which is isoelectronic with CO2 and N2O NaN3  Na (m) + 3/2N2 (g)

  16. Pourbaix diagrams

  17. P oxides

  18. Phosphates

  19. P oxides mostly strong reducing agents (except for P(V)), especially in base Generally labile reactions Ox state +1 H2PO2 (hypophosphite) H3PO2 is monoprotic +3 HPO32 (phosphite) H3PO3 is diprotic +5 PO43 (phosphate) Td H3PO4 is triprotic Anhydride acid P4O6 H3PO3 P4O10 H3PO4 H2O

  20. Sb2O4

  21. PS compounds Matches: P4S3 + KClO3 + filler/glue/water = strike anywhere KClO3 (head) and red P (stripe) = safety P4S3

  22. Note that –P=N- is isoelectronic with –Si=O- (siloxanes) nPCl3 + nNH4Cl  (Cl2PN)n + 4n HCl n = 3 or 4 dichlorophosphazene trimer or tetramer oligomer  290 C + Lewis acid initiator (Cl2PN)n polydichlorophosphazene, elastomeric at RT  2n NaOR (can be OR , NR2) [(RO)2PN]n 130 C PN compounds These hydrolyze in air to form phosphate and HCl P4(NR)6 planar but not aromatic An air stable poly-phosphazene

  23. Arsine ligand 4 As + 6 CH3I → 3 (CH3)2AsI + AsI3 (CH3)2AsI + Na → Na+(CH3)2As- + NaI Na+(CH3)2As- → o-C6H4(As(CH3)2)2 soft LB, bidentate o-C6H4Cl2 / THF [PdCl6]2-

  24. Organoarsine chemistry As(CH3)3 + CH3Br → As(CH3)4+Br- oxidative addition As(III) -> As(V) For As(Ph)3 , this does not work Ph3As=O + PhMgBr → Ph4As+Br- + MgO acid-base exchange (Td) LiPh AsPh5 + LiBr

  25. As-As bonding 2As(CH3)2Br + Zn → (CH3)2As-As(CH3)2 + ZnBr2 As5(CH3)5

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